1. Field of the Invention
The present invention relates to self-crosslinkable film-forming compositions, and to the use of such compositions in a process for preparing multi-layered coated articles comprising a pigmented or colored base coat and a transparent or clear topcoat.
2. Brief Description of the Prior Art
Color-plus-clear coating systems involving the application of a colored or pigmented base coat to a substrate followed by the application of a transparent or clear topcoat to the base coat have become conventional as original finishes for automobiles. The clear coat imparts outstanding gloss and distinctness of image (DOI) to the color-plus-clear systems, and serves to protect the base coat from environmental attack.
Because many geographic areas encounter acidic precipitation, resistance to etching by atmospheric acid precipitation ("acid etch resistance") is becoming an increasingly desirable property for coatings, particularly automotive original equipment coatings. Original equipment manufacturers are requiring that coating systems demonstrate acid etch resistance. In response to this requirement, coating compositions based on functional polymers cured with a crosslinking agent have been developed for use in color-plus-clear coating systems.
Coatings cured with aminoplast crosslinking agents such as polymeric polyol-aminoplast systems are known to provide many excellent coating properties. They are inexpensive, durable, and attractive. However, it is widely recognized that such coatings, particularly clear coats, have poor resistance to etching by atmospheric acidic pollutants. Polymeric polyol-aminoplast coating systems of the prior art are not highly effective for providing protection against etching caused by acid rain.
Clear coat compositions comprising polyols such as polyester polyols, polyurethane polyols, and acrylic polyols cured with polyisocyanate crosslinking agents yield coatings with outstanding gloss and distinctness of image. However, such systems do not provide optimum mar and abrasion resistance. In addition, the isocyanates are difficult to handle because they are sensitive to moisture and require cumbersome safety precautions because of their toxicity.
It would be desirable to provide a color-plus-clear coating system which avoids the problems of the prior art by providing improved acid etch resistance and mar resistance properties, and which does not have the drawbacks associated with crosslinking agents of the prior art.